Dual Vacancy-Driven "Lattice Softening" NiFeAl_x LDHs for High-Rate and Durable Chloride Ion Storage

Defect engineering becomes an essential strategy for enhancing electrochemical performance, yet its application in anion-based systems such as chloride-ion batteries (CIBs) remains largely unexplored. Herein, a rational defect-engineering strategy is developed to overcome these bottlenecks by constructing dual-vacancy NiFeAl_x layered double hydroxides (LDHs) featuring coexisting cationic and oxygen vacancies, achieved via a room-temperature alkaline etching process that selectively leaches Al³⁺ while retaining layered integrity. The optimized NiFeAl_0.04-24h-Cl LDH exhibits unprecedented "lattice softening" behavior, enabling elastic deformation and dynamic structural reconstruction to accommodate volumetric fluctuations during Cl-intercalation/de-intercalation. Benefiting from this defect-induced structural flexibility, the electrode delivers a high reversible capacity of 101.4 mAh g^-1 after 1000 cycles at 1000 mA g^-1, along with the Coulombic efficiency of 99.91%. Multiscale mechanistic analyses demonstrate that the coupled vacancies regulate local electronic distribution and coordination environments while simultaneously imparting pronounced lattice softening and structural elasticity to the NiFeAl_0.04-24h-Cl LDH, thereby facilitating enhanced Cl^- ion accommodation. Furthermore, the vacancies construct interconnected 3D ion highways, which dramatically accelerate Cl^- diffusion, enhance interfacial adsorption kinetics, and minimize charge-transfer resistance. Such lattice-adaptive regulation resolves the long-standing trade-off between anion-storage capacity and structural stability in LDH-based systems, offering a promising strategy for designing efficient anion-hosting electrodes for advanced CIB systems.